The goal of this research is to investigate the neural mechanisms which underlie adults'ability to acquire new phonetic categories. Specifically, we will investigate how experience with statistical and referential properties of the input shapes subjects'perceptual sensitivities to items along an acoustic-phonetic continuum, and the neural correlates of these changes in sensitivity. This will be accomplished by using functional MRI (fMRI) to measure activation patterns in adult subjects who have been familiarized with auditory stimuli taken from a non-native phonetic continuum. Importantly, the statistical distribution of the auditory stimuli presented during familiarization, as well as the visual/referential cues which accompany the auditory stimuli will be varied in order to isolate neural correlates of statistical and referential cues to phonetic category identity. Sensitivity of neural structures to equivalent acoustic intervals at different locations along the continuum will be probed using a short-interval habituation paradigm, in which release from adaptation of the fMR signal is used as a marker for neural sensitivity to changes in phonetic category structure. It is argued that changes in activation as a function of familiarization in such areas as the posterior superior temporal gyrus would suggest that the changes in phonetic category structure are mediated early in the phonetic processing stream. Alternatively, changes in activation in the frontal (inferior frontal gyrus) and parietal (supramarginal gyrus, angular gyrus) structures would suggest that the warping of phonetic categories occurs later in the processing stream and reflects the recruitment of attentional, lexical, or executive systems. Results will shed light on the process by which statistical and referential cues shape perceptual sensitivities which ultimately form the basis of phonetic categories. Relevance: The proposed research will shed light on the neural mechanisms which underlie the acquisition of phonetic categories, and may ultimately be used to inform treatment strategies for children with developmental language disorders. Additionally, results should add to our understanding of the neural bases of speech processing in adults, which may be used to suggest rehabilitative strategies for aphasic patients who have suffered language impairments due brain injury.